Prior art optical devices include many types of magnifiers, telescopes, and telemicroscopes prescribed to assist the normally sighted and the visually impaired, for example, people with poor vision, to see objects at a distance and close up. Almost all of the existing telescopes designed for the visually impaired are conventional Galilean-type or terrestrial Keplerian-type telescopes. Typically, these conventional telescopes have restricted fields of view that depend mainly on their magnification, degree of optical correction, and the corresponding complexity of their optical design. For example, the field of view (FOV) of a Galilean telescope depends on the diameter of its objective lens. However, increasing the lens diameter of a Galilean telescope exponentially increases the transverse spherical aberration and coma, two common forms of optical aberration. In order to control spherical aberration, coma, and chromatic aberration, conventional telescope designers typically resort to complex objective lenses that, for example, may comprise two or more elements or aspheric surfaces. However, because the angular field of the ocular lens, or eye piece, is equal to the angular field of the objective lens multiplied by the magnification of the telescope, such complex objective lenses often result in an even greater growth in the off-axis aberrations such as coma, astigmatism and field curvature. These aberrations can typically only be corrected by employing a multi-element eyepiece. Thus, as the field is increased, the correction of compound systems such as telescopes and telemicroscopes becomes increasingly complex, and the devices become ever more costly and bulky.
A study of low vision telescopes by Katz, et al. [“Optical Properties of low vision telescopes.” 1987, Journal of the American Osteopathic Association, 54(4), 320-31] reported the following fields of view for Galilean telescopes:
MagnificationTotal Apparent Field of View (FOV)2.121.8 degrees2.911.1 degrees3.712.1 degreesMeade Instruments, a major manufacturer of telescopes, makes 4×30 Galilean binocular that has a 16.5° total apparent field [see http:www.solarobjects/]. Aspects of the present invention provide an apparent field of view greater than that what is presently provided by the prior art. For example, aspects of the invention can provide a 2× Galilean-type telescope having a magnification of 2 and an apparent FOV of greater than 70 degrees, that is, more than triple the FOV of the prior art 2.1× telescopes in the above Table.
With respect to low distance vision impairment, Faye [Clinical Low Vision, 1967, Little Brown and C., Boston, pp. 67, 72, 139, 238] states, “The best practice is for the doctor to prescribe a telescope that will offer the patient the widest field rather than the highest magnification.” Increasing the field coverage of telescopes and telemicroscopes offers several advantages. The widened fields improve the ability to search for and acquire objects of interest, for example, a street signs. Seeing the spatial relationships of objects in different parts of the field are improved by widened fields. Aspects of the invention provide these widened fields of view.
Aspects of the present invention also facilitate following moving targets, for example, even following the flight of birds. Other aspects of the invention providing a bioptic array will help the ambulatory user to avoid hazards in the peripheral field. Aspects of the present invention that provide wide peripheral field coverage will be especially useful to patients with central vision loss, hemianopsia, etc.
Bioptic telescopes are used by visually impaired drivers. It has been noted by Owsley, et al. [“Vision impairment and driving,” Survey of Ophthalmology, 1999, May-June, 43 (6): 535-550] that visual acuity is only “weakly related to crash involvement, whereas peripheral vision appears to play a more critical role.” Aspects of the present invention will offer increased peripheral vision and reduce search time for finding and reading traffic signs, thus, potentially resulting in safer driving.
With respect to near vision impairment, most people with low vision require magnification to read. A magnifying lens's field of view often contains only a few letters at a time. Page navigation is the process by which the reader moves the magnifier from word to word and from the end of one line to the beginning of the next line. As noted by Beckmann, et al. [“Psychophysics of Reading—XIV, The page navigation problem in using magnifiers” Vision Research, 1996 November 36(22) 3723-3733], page navigation takes time and reduces reading speed. Legge, at al. [“Psychophysics of Reading—XVI, The visual span in normal and low vision,” Vision Research, 1997 July: 37(14) 1999-2010] note that there is a strong dependence of reading time on word length. Aspects of the present invention can be converted for near vision tasks with lens caps.
Faye [Ibid.] notes that the gain in reading from optical aids is limited by the dimensions of the patient's field at the working distance of the aid. Employing aspects of the present invention, reading and near tasks will become more normal with widened fields. For example, employing aspects of the present invention, entire lines of text may be scanned, and progressing to the next line of text will be improved.
Working distance is an important characteristic of prior art telemicroscopes. As with all telemicroscopes, the working distance will be significantly greater than with a simple magnifier. For example, a 4× telescope with a 2× cap will have a magnification of 8× and a working distance of 125 mm compared with a working distance of 31 mm for an 8× magnifier. Aspects of the present invention can facilitate reading because the lower spatial frequencies of magnified text provided by aspects of the present invention may increase the tolerance to defocus. As noted by Legge, et al. [“Tolerance to visual defocus”, Journal of the Optical Society of the American Medical Association, 1987 May: 4(5): 851-863], individuals with low acuity are more tolerant to defocus than people with normal vision.
Thus, a need exists for optical devices that provide an improved field of view that can, among other things, improve distance vision and near vision, for the visually impaired and the non-visually impaired.